1. Field of the Invention
The present invention relates to an electret condenser microphone and a method of producing the same available for various audio equipments such as a cellular phone, and more particularly to an electret condenser microphone and a method of producing the same equipped with a condenser unit constituted by an electrode plate and a diaphragm to receive an acoustic wave to be converted to an acoustic signal indicative of the acoustic wave.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of conventional electret condenser microphones each equipped with a condenser unit constituted by an electrode plate and a diaphragm to receive an acoustic wave to be converted to an acoustic signal indicative of the acoustic wave.
The conventional electret condenser microphones of this type have so far been available for various audio equipments such as a cellular phone. One typical example of the conventional electret condenser microphones is exemplified and shown in FIGS. 8 and 9. The conventional electret condenser microphone 900 thus proposed comprises a casing member 910 having a center axis 911. The casing member 910 includes a circular acoustic inlet portion 912, and a cylindrical side portion 913 integrally formed with the acoustic inlet portion 912. The acoustic inlet portion 912 of the casing member 910 has thereon an electret film 916 to constitute an electrode plate. The side portion 913 of the casing member 910 has a first section 914 close to the acoustic inlet portion 912 of the casing member 910, and a second section 915 remote from the acoustic inlet portion 912 of the casing member 910 and radially inwardly bent toward the center axis 911 of the casing member 910.
The conventional electret condenser microphone 900 further comprises a covering member 920 provided on the acoustic inlet portion 912 of the casing member 910, and a printed circuit board 960 disposed in the casing member 910 and spaced apart along the center axis 911 of the casing member 910 from the acoustic inlet portion 912 of the casing member 910. The printed circuit board 960 is partly held in contact with the second section 915 of the side portion 913 of the casing member 910.
The conventional electret condenser microphone 900 further comprises an electrically connecting member 940 provided on the printed circuit board 960, and a diaphragm 930 provided on the electrically connecting member 940. The diaphragm 930 includes a peripheral portion 931 securely retained by the electrically connecting member 940, and a central portion 932 integrally formed with the peripheral portion 931 and radially inwardly extending from the peripheral portion 931 to be partly oscilatable along the center axis 911 of the casing member 910 with respect to the casing member 910. The acoustic inlet portion 912 of the casing member 910 is formed with a plurality of acoustic apertures 917 to have the acoustic wave transmitted to the diaphragm 930 through the covering member 920 and the acoustic apertures 917 of the acoustic inlet portion 912 of the casing member 910. The electrically connecting member 940 is made of a metal and intervenes between the printed circuit board 960 and the peripheral portion 931 of the diaphragm 930 to have the printed circuit board 960 and the peripheral portion 931 of the diaphragm 930 electrically connected with each other.
The conventional electret condenser microphone 900 further comprises an electrically insulating spacer 950 partly intervening between the acoustic inlet portion 912 of the casing member 910 and the diaphragm 930 to have the acoustic inlet portion 912 of the casing member 910 and the diaphragm 930 spaced apart from each other at a predetermined space distance. The acoustic inlet portion 912 of the casing member 910, i.e., the electrode plate, and the diaphragm 930 collectively constitute a condenser unit 933 to generate an electrical capacitance corresponding to the space distance between the acoustic inlet portion 912 of the casing member 910 and the diaphragm 930 when the acoustic wave is transmitted to the diaphragm 930 to have the central portion 932 of the diaphragm 930 partly oscillated along the center axis 911 of the casing member 910 with respect to the casing member 910.
The conventional electret condenser microphone 900 further comprises a signal converting unit 970 including a field effect transistor 971 and designed to convert the electrical capacitance generated by the condenser unit 933 to the acoustic signal indicative of the acoustic wave transmitted to the diaphragm 930. The signal converting unit 970 is provided on the printed circuit board 960 to be electrically connected to the acoustic inlet portion 912 of the casing member 910 through the printed circuit board 960 and the side portion 913 of the casing member 910, and to the diaphragm 930 through the printed circuit board 960 and the electrically connecting member 940.
The following description will be directed to a method of producing the conventional electret condenser microphone 900 with reference to the drawings shown in FIGS. 10A, 10B and 10C. The method of producing the conventional electret condenser microphone 900 is performed through the steps including a preparing step, an imparting step and a releasing step as follows.
In the preparing step, the casing member 910, the covering member 920, the printed circuit board 960, the electrically connecting member 940, the diaphragm 930, the electrically insulating spacer 950, and the signal converting unit 970 are prepared as a partially fabricated unit. The second section 915 of the side portion 913 of the previously mentioned casing member 910 is straightly extends from the first section 914 of the side portion 913 of the casing member 910.
In the imparting step, the second section 915 of the side portion 913 of the casing member 910 is then imparted an external force toward an imparting direction shown by an arrow 901 to assume a first state in which the second section 915 of the side portion 913 of the casing member 910 is bent toward the center axis 911 of the casing member 910 as shown in FIG. 10B.
In the releasing step, the second section 915 of the side portion 913 of the casing member 910 is then released from the external force imparted thereto toward the imparting direction shown by the arrow 901 to assume a second state in which the second section 915 of the side portion 913 of the casing member 910 is naturally elastically restored along the center axis 911 of the casing member 910. The conventional electret condenser microphone 900 is then produced as shown in FIG. 10A.
The conventional electret condenser microphone, however, encounters such a problem that each of the second section 915 of the side portion 913 of the casing member 910 and the electrically connecting member 940 is spaced apart from the printed circuit board 960 in the releasing step as shown in FIG. 10C, resulting from the fact that the second section 915 of the side portion 913 of the casing member 910 is prevented by the electrically connecting member 940 made of a metal from being deformed toward the imparting direction shown by the arrow 901 as shown in FIG. 10B, and the second section 915 of the side portion 913 of the casing member 910 is naturally elastically restored along the center axis 911 of the casing member 910 as shown in FIG. 10C.
The fact that each of the second section of the side portion of the casing member and the electrically connecting member is spaced apart from the printed circuit board leads to the fact that each of the acoustic inlet portion of the casing member, i.e., the electrode plate, and the diaphragm is electrically disconnected from the printed circuit board.
It is therefore an object of the present invention to provide an electret condenser microphone which is constructed to ensure that each of the electrode plate and the diaphragm is electrically connected with the printed circuit board.
It is another object of the present invention to provide a method of producing an electret condenser microphone which is constructed to ensure that each of the electrode plate and the diaphragm is electrically connected with the printed circuit board.
In accordance with a first aspect of the present invention, there is provided an electret condenser microphone for receiving an acoustic wave to be converted to an acoustic signal indicative of said acoustic wave, comprising: a casing member having a center axis and including a circular acoustic inlet portion and a cylindrical side portion integrally formed with the acoustic inlet portion, the side portion of the casing member having a first section close to the acoustic inlet portion of the casing member and a second section remote from the acoustic inlet portion of the casing member, the second section of the side portion of the casing member radially inwardly bent toward the center axis of the casing member, a printed circuit board disposed in the casing member and held in contact with the second section of the side portion of the casing member, the casing member and the printed circuit board collectively forming a cylindrical casing space; an electrically insulating member accommodated in the casing space and provided on the printed circuit board; an electrode plate provided on the electrically insulating member; and an electrically connecting member intervening between the printed circuit board and the electrode plate to have the printed circuit board and the electrode plate electrically connected with each other.
The outer diameter of the electrically connecting member may be less than the inner diameter of the second section of the side portion of the casing member.
The electrically insulating member may form part of an annular groove open toward the side portion of the casing member, and the inner diameter of the annular groove may be less than the inner diameter of the second section of the side portion of the casing member.
The electret condenser microphone may further comprise a diaphragm supporting member accommodated in the casing space and provided on the acoustic inlet portion of the casing member; and a diaphragm including a peripheral portion securely retained by the diaphragm supporting member and a central portion integrally formed with the peripheral portion and radially inwardly extending from the peripheral portion to be partly oscilatable with respect to the casing member, the diaphragm opposing and spaced apart from the electrode plate at a predetermined space distance.
The electret condenser microphone may further comprise an electrically insulating spacer intervening between the electrode plate and the diaphragm to have the electrode plate and the diaphragm spaced apart from each other at the predetermined space distance.
The electrode plate and the diaphragm may collectively constitute a condenser unit to generate an electrical capacitance corresponding to the space distance between the electrode plate and the diaphragm when the acoustic wave is transmitted to the diaphragm to have the central portion of the diaphragm partly oscillated with respect to the casing member.
The electret condenser microphone may further comprise signal converting means for converting the electrical capacitance generated by the condenser unit to the acoustic signal indicative of the acoustic wave transmitted to the diaphragm.
The signal converting means may include a field effect transistor, a chip capacitor and a resistor.
The electret condenser microphone may further comprise a covering member provided on the acoustic inlet portion of the casing member.
The electrode plate may have thereon an electret film.
In accordance with a second aspect of the present invention, there is provided a method of producing an electret condenser microphone, comprising the steps of: preparing a partially fabricated unit comprising a casing member having a center axis and including a circular acoustic inlet portion and a cylindrical side portion integrally formed with the acoustic inlet portion, the side portion of the casing member having a first section close to the acoustic inlet portion of the casing member and a second section remote from the acoustic inlet portion of the casing member, a printed circuit board disposed in the casing member and spaced apart from the acoustic inlet portion of the casing member, the casing member and the printed circuit board collectively forming a cylindrical casing space, an electrically insulating member accommodated in the casing space and provided on the printed circuit board, an electrode plate provided on the electrically insulating member, an electrically connecting member intervening between the printed circuit board and the electrode plate to have the printed circuit board and the electrode plate electrically connected with each other; imparting an external force to the second section of the side portion of the casing member to assume a first state in which the second section of the side portion of the casing member is bent toward the center axis of the casing member to the extent that the electrically insulating member is forcibly elastically deformed along the center axis of the casing member; and releasing the second section of the side portion of the casing member from the external force imparted thereto to assume a second state in which the second section of the side portion of the casing member is naturally elastically restored along the center axis of the casing member to the extent that the electrically insulating member is naturally elastically restored along the center axis of the casing member.
The electrically insulating member may be made of a resin.